• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.6 s.40
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• pp.73-80
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• 2004

A nonlinear time-domain system identification algorithm using measured acceleration data is developed for structural damage assessment. To take account of nonlinear behavior of structural systems, an output error between measured and computed acceleration increments has been defined and a constrained nonlinear optimization problem is solved for optimal structural parameters. The algorithm estimates time-varying properties of stiffness and damping parameters. Nonlinear response of restoring force of a structural system is recovered by using the estimated time-varying structural properties and computed displacement by Newmark-$\beta$ method. In the recovery, no pre-defined model for inelastic behavior has been assumed. In developing the algorithm, noise and incomplete measurement in space and state have been considered. To examine the developed algorithm, numerical simulation and laboratory experimental studies on a three-story shear building have been carried out.

• Journal of Korea Water Resources Association
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• v.52 no.11
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• pp.887-894
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• 2019

We proposed a GPU (Grapic Processing Unit) accelerated kinematic wave model for rainfall runoff simulation and tested the accuracy and speed up performance of the proposed model. The governing equations are the kinematic wave equation for surface flow and the Green-Ampt model for infiltration. The kinematic wave equations were discretized using a finite volume method and CUDA fortran was used to implement the rainfall runoff model. Several numerical tests were conducted. The computed results of the GPU accelerated kinematic wave model were compared with several measured and other numerical results and reasonable agreements were observed from the comparisons. The speed up performance of the GPU accelerated model increased as the number of grids increased, achieving a maximum speed up of approximately 450 times compared to a CPU (Central Processing Unit) version, at least for the tested computing resources.

• Journal of Navigation and Port Research
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• v.43 no.3
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• pp.197-208
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• 2019

This paper assessed the impacts of the specification of the yard, handling equipment, and operation approaches on the expected number of re-handles during the loading operation for empty containers. When the various types of empty containers from multiple shipping liners are placed in separate spaces from each other, then the storage space cannot be fully utilized. So as to increase the utilization of the storage space, empty containers from multiple vessel liners are stored together incurring additional re-handles during the loading operation. Several formulas are derived for the estimation of the expected number of handles, including re-handles, for empty container retrieval from a bay. Transfer cranes and top handlers are utilized as handling equipment and various retrieval strategies are examined. Numerical analysis was conducted to assess the effects of various designs and operational parameters of the container stacking yard on the expected number of handles.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.6
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• pp.102-112
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• 2020

In this study, in order to design a wedge-type anchor that can hold an wide carbon plate with a width of 100 mm or more that can be used in a bridge structure, the mechanical behaviors are evaluated based on the main design variables such as the angle of the wedge and the coefficient of friction between the guide and the wedge. The stress state of the carbon plate was calculated by numerical analysis method for each design variable, and the performance of the anchor in the critical state was evaluated according to the failure criteria for composite material, and the optimal design specifications of the anchor were determined based on numerical results. The performance of the optimally designed anchor was verified through actual experiments, and the results of this study are considered to be useful for the optimal design of the CFRP plate anchor to reinforce large structures.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6D
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• pp.663-673
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• 2009

Driver's perceived curve radius is different from actual curve radius at curve sections. This is called visual distortion. It has effect on operation speed according to driver's perception and finally bad effect on safety at curve sections. At present, however, there is no research on quantitatively analysis of visual distortion and no criteria for curve section design considering the visual distortion. Therefore, this study focus on finding degree of visual distortion and suggesting design criteria by visual distortion analysis. The process of this study is as below; First, a calculaiton model of perceived curve radius was developed by survey using computer simulation. In this model, a dependent variable is perceived curve radius and an independent variable is geometric factors. Second, degree of visual distortion was calculated from ratio of perceived curve radius to actual curve radius. Finally, design criteria were suggested through influencing factor analysis of visual distortion at curve sections.

• Survey Research
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• v.12 no.3
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• pp.49-62
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• 2011

In this paper we investigate design-based properties of both the ordinary least square estimator and the weighted least square estimator for regression coefficients in panel regression model. We derive formulas of approximate bias, variance and mean square error for the ordinary least square estimator and approximate variance for the weighted least square estimator after linearization of least square estimators. Also we compare their magnitudes each other numerically through a simulation study. We consider a three years data of Korean Welfare Panel Study as a finite population and take household income as a dependent variable and choose 7 exploratory variables related household as independent variables in panel regression model. Then we calculate approximate bias, variance, mean square error for the ordinary least square estimator and approximate variance for the weighted least square estimator based on several sample sizes from 50 to 1,000 by 50. Through the simulation study we found some tendencies as follows. First, the mean square error of the ordinary least square estimator is getting larger than the variance of the weighted least square estimator as sample sizes increase. Next, the magnitude of mean square error of the ordinary least square estimator is depending on the magnitude of the bias of the estimator, which is large when the bias is large. Finally, with regard to approximate variance, variances of the ordinary least square estimator are smaller than those of the weighted least square estimator in many cases in the simulation.

• Journal of Korean Society of Forest Science
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• v.109 no.1
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• pp.50-61
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• 2020

Street trees are very important to urban environments as they can alleviate air pollution. However, when ozone is absorbed through the stomata, it can induce the formation of free radicals inside the tree, negatively affecting the vegetation. The present study investigated the Air Pollution Tolerance Index (APTI) of four major street tree species: Prunus yedoensis, Zelkova serrata, Chionanthus retusus, and Pinus densiflora. Two-year-old seedlings were placed in a phytotron and fumigated with 100 nL·L^-1 (ppb) ozone for 4 weeks, following which the ascorbic acid contents, chlorophyll contents, leaf pHs, and relative water contents were measured. There was no significant difference in the APTI of Prunus yedoensis and Zelkova serrata between the ozone and control treatments. By contrast, the ozone treatment caused the APTI of Chionanthus retusus to increase and that of Pinus densiflora to decrease compared with the respective controls. These results suggest that the APTI of these tree species exhibit very different responses to ozone. Therefore, more detailed research should be conducted on a range of species in the future.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.2
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• pp.103-108
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• 2019

Non-equilibrium molecular dynamics simulation on the thermal boundary resistance(TBR) of an aluminum(Al)/silicon(Si) interface was performed in the present study. The constant heat flux across the Si/Al interface was simulated by adding the kinetic energy in hot Si region and removing the same amount of the energy from the cold Al region. The TBR estimated from the sharp temperature drop at the interface was independent of heat flux and equal to $5.13{\pm}0.17K{\cdot}m^2/GW$ at 300K. The simulation result was experimentally confirmed by the time-domain thermoreflectance technique. A 90nm thick Al film was deposited on a Si(100) wafer using an e-beam evaporator and the TBR on the film/substrate interface was measured using the time-domain thermoreflectance technique based on a femtosecond laser system. A numerical solution of the transient heat conduction equation was obtained using the finite difference method to estimate the TBR value. Experimental results were compared to the prediction and discussions on the nanoscale thermal transport phenomena were made.

• Tunnel and Underground Space
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• v.25 no.2
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• pp.186-198
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• 2015

This paper aims for the ultimate goal to optimize the work place environment through assuring the optimal required ventilation rate based on the analysis of the airflow. The working environment is deteriorated due to a rise in temperature of a coal mine caused by increase of its depth and carriage tunnels. To improve the environment, the ventilation evaluation on J coal mine is carried out and the effect of a length of the tunnel on the temperature to enhance the ventilation efficiency in the subsurface is numerically analyzed. The analysis shows that J coal mine needs $17,831m^3/min$ for in-flow ventilation rate but the total input air flowrate is $16,474m^3/min$, $1,357m^3/min$ of in-flow ventilation rate shortage. The temperatures were predicted on the two developed models of J mine, and VnetPC that is a numerical program for the flowrate prediction. The result of the simulation notices the temperature in the case of developing all 4 areas of -425ML as a first model is predicted 29.30 at the main gangway 9X of C section and in the case of developing 3 areas of -425ML excepting A area as a second model, it is predicted 27.45 Celsius degrees.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.15 no.1
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• pp.39-50
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• 2003

This study aims to figure out water quality impacts due to sudden disturbances of sediments during dike construction in land reclamation for the northern part of the Siwhaho Lake where heavily deteriorated settlements from upstream loadings are outstanding. We exploit a 3-D water quality model CE-QUAL-ICM combined with a hydrodynamic model TIDE3D. Simulations are done accounting water-sediment interaction in a 4-$\sigma$ layers. Long-term simulation for 1-year shows that bottom layers around the disturbance location are only affected and marks very high concentration. Complete vertical mixing appears at least 5km apart to downward due to complex effects of geometry, bathymetry and river inflows. It should be addressed that existing condition of the Siwhaho Lake stands for high concentration of COD and TP in winter and spring due to relatively high incoming loadings, however the effect of sediment disturbances yields reverse phenomena, i.e., impacts of dike construction arise greatly in summer and fall. Refined grid system consisting of 150m${\times}$150m rectangular grid, which is doubled system compared to previous study (Suh et al.,2002), gives affordable results by reducing flux differences through a cell especially in front of gate.